Volunteers in bright yellow get ready prior to the London Marathon in the Mall in London, Sunday, April 21, 2013. Security has been stepped up in London following the recent bombs at the Boston Marathon. The London Marathon started as planned on a glorious sunny morning Sunday despite concerns raised by the bomb attacks on the Boston Marathon six days ago. (AP Photo/Alastair Grant)

British police officers gather at the start at Blackheath during the London Marathon in London, Sunday, April 21, 2013. The London Marathon started as planned on a glorious sunny morning Sunday despite concerns raised by the bomb attacks on the Boston Marathon six days ago. (AP Photo/Sang Tan)

British police officers make final checks in the Mall, prior to the beginning of the London Marathon near to the finish line for marathon is situated in London, Sunday, April 21, 2013. Security has been stepped up in London following the recent bombs at the Boston Marathon. The London Marathon started as planned on a glorious sunny morning Sunday despite concerns raised by the bomb attacks on the Boston Marathon six days ago. (AP Photo/Alastair Grant)

Mai Ito of Japan, left, Yoko Shibui of Japan, fourth left, and Remi Nakazato of Japan, right, start the elite women race during the London Marathon in London, Sunday, April 21, 2013. The London Marathon started as planned on a glorious sunny morning Sunday despite concerns raised by the bomb attacks on the Boston Marathon six days ago. (AP Photo/Sang Tan)

The elite women's marathon runners start their race during the London Marathon, London, Sunday, April 21, 2013. The London Marathon started as planned on a glorious sunny morning Sunday despite concerns raised by the bomb attacks on the Boston Marathon six days ago. (AP Photo/Sang Tan)

Thousands of runners who took part in the London Marathon on Sunday paid tribute to those killed and injured in the Boston Marathon six days earlier. Participants paused for a moment of silence in the beginning, many wore black ribbons on their chests as a sign of solidarity, and two runners finished carrying a banner that read "For Boston."

The mood was festive, defiant — and the surging crowds who turned out on the glorious spring day to line the route roared enthusiastically.

"It means that runners are stronger than bombers," said Valerie Bloomfield, a 40-year-old participant from France.

London's is the first major international marathon since two bombs exploded near the finish line in Boston. The blasts killed three people and wounded 180, and a policeman died during the search for the bombers. One suspect died in a shootout with police, while a second was caught.

Some 35,000 runners took part in the London race, which also drew tens of thousands of spectators — many regulars said it was the biggest and most enthusiastic crowd in years. Many said they made a point of turning up to show they were not afraid.

"We can't look back. We must look forward," said Tomasz Hamerlak of Poland, who finished fourth in the men's wheelchair race and who had competed in Boston last week. "The show must go on."

Authorities in London boosted the police presence by 40 percent and adding extra surveillance as precautionary measures, but in the end all went peacefully.

Mark Cliggett, from Seattle, was back on the track Sunday after witnessing the attack in Boston. Cliggett, 51, said he was within 200 meters of the finishing line there when the bombs exploded.

"Last week was horrible, and people's lives have been changed in ways that can't be undone," he said after completing the London race. "I wanted to come out and just show: No, we're going to keep running, we're going to keep doing this."

Stuart Calderwood, an editor with a New York running magazine who has run in eight Boston Marathons, said that the recent carnage there made him and his friends more determined to run in London.

"My group that came here, we just decided this is going to make us better. We're going to say marathons are the opposite of bombing and hostility and terror," Calderwood, 55, said after finishing.

Londoners pride themselves on their resilience: A day after the lethal July 7, 2005, transit system bombings that killed 52 commuters, many came back onto the streets and resumed their normal routines.

Still, some acknowledged an undercurrent of anxiety Sunday. Chris Denton, a 44-year-old engineer, said he had asked that his family not come out to support him because of a possible copycat attack. "I left them at home," he said. "If only for my peace of mind."

The men's race was won by Ethiopian Tsegaye Kebede; the women's champion was Kenyan Priscah Jeptoo.

A seemingly relaxed Prince Harry presented awards to the wheelchair racers and mingled with spectators.

"It's fantastic, typically British," he told the BBC. "People are saying they haven't seen crowds like this for eight years around the route. It's remarkable to see."

He said it was "never an option" for him to cancel his appearance following the Boston bombings.

"No one has changed any plans, volunteers, security, nothing has changed," he said. "Typically the British way."

On Blackheath, the spacious green common area where the race begins, runners massaged each other's legs as loud pop music boomed on a sound system. A half-dozen police officers in reflective vests mingled and chatted with the runners. Many in the crowd wore Boston T-shirts.

Moments before the majority of runners set off on the grinding course, announcer Geoff Wightman used the loudspeakers to ask for a moment of silence. He described marathon running as a global sport that unites runners and supporters in every continent in a spirit of friendship.

As those gathered responded to his call, the only noise that could be heard was the buzz of helicopters and the beeping of a truck.

Security was plentiful but not intrusive near the finish line at the Mall in front of Buckingham Palace. Marathon staff, officials and journalists had their bags checked, a process not deemed necessary at the event last year. Officials said this was in response to the Boston attack.

Marathon organizers plan to donate money to a Boston fund set up to help the bombing victims. They said they did not consider canceling the London event, which is a highlight of the sporting calendar.

In a smaller event in Germany, some 15,000 runners participated Sunday in the Hamburg Marathon. They wore armbands with the slogan "Run for Boston."

Extra security was added and there was no disruption. Hamburg organizers have said that they know of only eight people who pulled out because of the Boston bombings.

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AP writer Rob Harris in London and Geir Moulson in Berlin contributed to this report.